Hi, Ken
If you just arm the motor but the motor not spin, the curren may not influence the mag cause the current is low, but with the prop, push the throtlle, the motor will drop huge current from the battery, if the battery cable close to the mag, the current will cause the mag data drift. May be you can take a pic show your quad and the FC board.

Yesterday I was able to get the quad out to a large open field to better test the advanced functions. On one flight I was able to set autolevel and altitude hold so that both were working well and then set GPS position hold so that it stayed within a very small area at the set altitude for over 1 minute so I know the board is capable of doing what it should and the software is setup correctly.

After that I did a test of RTH and it did turn towards home and fly in that direction but never locked onto the actual home position, instead starting to circle in ever increasingly larger loops. Just before I turned the GPS off it started to head off in a straight line very fast after doing several loops trying to find home.

On a second flight autolevel and altitude hold worked well again however this time the GPS wouldn't stay in place, it circled around and shortly afterward started to fly off in a straight line again, this time I didn't fully regain control and it crashed breaking one of the arms, done for the day.

The problem does appear to be mag/compass related and given the frame setup the only thing I can do is either swap to another frame or move the board to the top frame plate as far away from power wires as I can get it and try again. Because it did hold position on one flight I know it does work but there is something causing inconsistant and unreliable performance, interference from power feeds could certainly do that so I now have to eliminate that as a potential problem, I'll let you know how it goes.

Yesterday I was able to get the quad out to a large open field to better test the advanced functions. On one flight I was able to set autolevel and altitude hold so that both were working well and then set GPS position hold so that it stayed within a very small area at the set altitude for over 1 minute so I know the board is capable of doing what it should and the software is setup correctly.

After that I did a test of RTH and it did turn towards home and fly in that direction but never locked onto the actual home position, instead starting to circle in ever increasingly larger loops. Just before I turned the GPS off it started to head off in a straight line very fast after doing several loops trying to find home.

On a second flight autolevel and altitude hold worked well again however this time the GPS wouldn't stay in place, it circled around and shortly afterward started to fly off in a straight line again, this time I didn't fully regain control and it crashed breaking one of the arms, done for the day.

The problem does appear to be mag/compass related and given the frame setup the only thing I can do is either swap to another frame or move the board to the top frame plate as far away from power wires as I can get it and try again. Because it did hold position on one flight I know it does work but there is something causing inconsistant and unreliable performance, interference from power feeds could certainly do that so I now have to eliminate that as a potential problem, I'll let you know how it goes.

Ken

Make sure the MAG is well calibrated otherwise the RTH will not work correctly. I think you can test the MAG with Headfree function if you can't visualize it without PC. If Headfree works well that means the MAG is correctly calibrated.

Make sure that the power cable is not near to the MAG. When huge current passes the MAG reading will be slightly changed.

Especially make sure the GPS module is on the top and nothing else is higher than it.

When all is in good condition you can start the PID settings. Be patient and you will find that it can fly better than any others because of the totally free tuning parameters.